Fiber Reinforced Polymer Plates Research Articles

Damage detection of thin plates by fusing variational mode decomposition and spectral entropy

This paper presents a new approach for damage detection in thin plates by fusing variational mode decomposition and spectral entropy (VMD-SE). In this method, after the received signal is decomposed into some intrinsic mode functions (IMFs) by variational mode decomposition (VMD), the spectral entropy ratio of the first and last IMFs is calculated for optimizing the VMD’s parameters and improving its decomposition performance. Moreover, the cross-correlation coefficient between the decomposed IMFs and the reference signal is computed to separate the desired IMF, which contains more damage information. Finally, the spectral entropy of the obtained IMF is calculated as an indicator for assessing the damage’s severity. The comparative analysis of the simulated signal clearly shows that only the proposed method can successfully separate the damage-related and reference signals. To verify the VMD-SE method, damage detection of two different types of damage on aluminum and composite fiber-reinforced polymer (CFRP) plates is conducted by using this new approach. The experimental results demonstrate that the parameters of VMD affect greatly its decomposition performance, and the best parameters are selected. The results also indicate that the normalized spectral entropy monotonically increases when the diameter of the through-hole or the length of the scratch increases. In addition, the correlation coefficients of the fitting lines of the plates are larger than 0.998. The experimental results of aluminum specimens demonstrate that the damage’s location has an influence on the normalized spectral entropy. At last, based on the linear relationship, the severity of damage in the fourth specimen is identified. The identification results demonstrate that the relative error of the aluminum and CFRP plates is less than 7.34%, which indicates that this new algorithm by fusing VMD and spectral entropy can detect the damage size in thin plates accurately and efficiently.

Measuring the in-plane thermal diffusivity of anisotropic solids by lock-in infrared thermography: Laser-spot vs laser-line heating

A method is proposed to measure the in-plane thermal diffusivity of anisotropic solids along an arbitrary direction using laser-line lock-in thermography. In this method, the sample is heated by an intensity-modulated laser beam, which impinges on the sample surface with the shape of a narrow strip. The resulting temperature oscillations are recorded by a thermographic camera and a phase thermogram is obtained by lock-in processing the image sequence. The thermal diffusivity along the direction perpendicular to the laser line can be determined from the linear dependence of phase lag with the distance to the heating line using the slope method. Unlike laser-spot lock-in thermography, in which the slope method only provides the thermal diffusivity along the principal directions, in this configuration, the thermal diffusivity can be measured experimentally along any direction, just selecting the relative orientation of the sample with respect to the laser line. Moreover, this configuration allows averaging several parallel phase profiles leading to more reliable thermal diffusivity values. The experimental results are presented for a highly anisotropic material, namely, a unidirectional carbon fiber-reinforced polymer plate.

Bond-Damaged Prestressed AASHTO Type III Girder-Deck System with Retrofits: Parametric Study

This research describes an in-depth analysis of the flexural strength of a strengthened AASHTO Type III girder-deck system with debonding-damaged strands based on the finite element software ABAQUS 6.17. To investigate the stand-debonding impact and retrofit, two strengthening techniques by the separate use of carbon fiber-reinforced polymer (CFRP) and steel plate (SP) were proposed. A detailed finite element analysis (FEA) model considering strand debonding, material deterioration, and retrofitting systems was developed and verified against relevant experimental data obtained by other researchers. The proposed FEA model and the experimental data were in good agreement. The sensitivity of the numerical model to the mesh size, element type, dilation angle and coefficient of friction was also investigated. Based on the verified FEA model, 156 girder-deck systems were studied, considering the following variables: (1) debonding level, (2) span-to-depth ratio (L/d), (3) strengthening type, and (4) strengthening material amount. The results indicated that the debonding level and span-to-depth ratio had a major effect on both load–deflection behaviors and the ultimate strength. The relationships between the enhancement of the ultimate strength and the thickness of the strengthening material were obtained through regression equations with respect to the CFRP- and SP-strengthened specimens. The coefficient of determination (R2) was 0.9928 for the CFRP group and 0.9968 for the SP group.

Flexural behaviour of bamboo scrimber beams with different composite and reinforced technology: A literature review

Bamboo scrimber (BS) is a novel renewable biocomposite material with excellent mechanical performance and stability that is suitable for load-bearing structural members. Beam-type components are among the most widely used members in structural engineering, and their flexural behaviour is crucial for the safety and applicability of structures. Based on a review of the existing literature, this article presents a comprehensive overview and discussion of the research and development of various forms of beam-type BS members with the aim of reaching a clearer understanding of the bending mechanisms and mechanical characteristics of BS beams. The members highlighted in this review include general BS beams, reinforced BS beams (with steel bars and fibre-reinforced polymer plates), composite BS beams (with profile steel and concrete), and strengthened damaged BS beams. Moreover, the factors affecting the flexural performance of BS beams, such as span-depth ratios, their mechanical properties, and reinforcing materials, are analysed quantitatively. Finally, the calculation models for the flexural bearing capacity and stiffness of BS beams are summarised and compared. This review aims to illustrate the potential of BS in the field of structural engineering and provide references for future research and design methods for BS flexural members.

Fracture research of adhesive-bonded joints for GFRP laminates under mixed-mode loading condition

Abstract The mixed-mode fracture characterization of adhesively bonded glass fiber-reinforced polymer (GFRP) plate joints is studied based on theoretical and experimental techniques. An improved beam model is used to estimate the compliance and the mixed-mode energy release rate (ERR) for GFRP four-point mixed-mode bending specimens. In this model, the deformation of the upper and lower GFRP plates is mutually independent, and the deformable adhesive is considered to satisfy the displacement compatibility conditions on the bonding interface. The explicit theoretical solutions of the compliance and ERR using the compliance method are reduced. The present theoretical solutions fit well with the finite element solutions by comparison with the rigid joint model. From the critical loads in experiment, the variation in fracture toughness on mixed-mode I/II has been determined by modifying the stiffness of the composite GFRP/GFRP substrate.

Performance of Carbon Fiber-Reinforced Polymer Plates Against Impact Loading

The carbon-fiber laminated composites are widely used in various industrial sectors due to their magnificent mechanical and engineering properties. While designing the structures of strategic importance, the impact perforation study and prediction of impact performance of such composites are of utmost importance. This work basically concentrates on two major areas of impact perforation study, determining impact perforation characteristics and understanding the perforation process. The objective has been achieved through experimental as well as numerical investigations. Microstructural analysis have also been carried out to understand different energy-absorbing mechanisms. The pneumatic gun setup is utilized to fire the projectile. In addition, square-shaped carbon fiber laminates and projectiles are modeled in ABAQUS/Explicit. The carbon fiber laminates of different thicknesses and layup sequences are impacted with three different types of projectiles. The cross ply, angle ply and quasi-isotropic layup sequences are considered in this study. The conical, blunt and ogive nose with caliber radius head (CRH) 1.5 projectiles are modeled as analytical rigid. Hashin criteria are adopted to replicate the behavior of carbon fiber laminates. The experimental and numerical calculations are compared and are found to be in good agreement. The different perforation features are calculated and the influence of ply orientations, thickness, projectile shape and impact velocities on the performance of targets against impact are discussed. An efficient and better laminate configuration under various ballistic conditions has been sought.

A full-range fatigue life prediction model for RC beams strengthened with prestressed CFRP plates accounting for the impact of FRP debonding

To predict the fatigue life of a reinforced concrete (RC) flexural member strengthened with externally bonded prestressed Fiber Reinforced Polymer (FRP) laminate accurately, the interaction between components with different degrees of degradation must be carefully taken into account. Furthermore, as the debonding of FRP plates is a recurrent problem, this has to be incorporated into the prediction model. In this study, a nonlinear analysis method for the entire process of fatigue damage in RC beams strengthened with prestressed Carbon Fiber Reinforced Polymer (CFRP) plates was proposed. In this model, all the components of the strengthened beam had independent fatigue degradation properties and failure criteria, and debonding growth was also explicitly considered. The comparison between the analytical and experimental results were used for model validation and good agreement was found.

A Note on Performance Assessment of Signal Energy–Based Acoustic Source Localization in a Carbon Fiber–Reinforced Polymer Plate

Abstract The effectiveness of the signal energy–based acoustic source localization approach in practical applications has yet to be established. This is addressed herein by conducting an experimental study on a 500 mm × 500 mm carbon fiber–reinforced polymer plate and generating artificial acoustic events in the plate. Upon acquiring the propagating wave signals at several well-scattered sensors, the signal energy–based approach is applied, and the accuracy of the source localization results is noted. Seven experiments are performed with varying source locations, sensor-plate bonding, and excitation types. This approach has performed well for five experiments with source localization errors below 15 mm. The remaining two experiments where the acoustic sources are relatively close to the plate edges compared to the other experiments have, however, produced large localization errors, indicating a scope of improvement in the approach to encompass all situations.

Repairing Behaviors of Cracked Steel Plates Based on Bolted Fiber-Reinforced Polymer Plates.

The use of FRP materials to repair cracked/damaged steel structures has gradually been adopted by researchers. This paper investigates the repairing effect of bolted FRP plates for cracked steel plates based on experimental and numerical simulation methods. In the experimental investigation, the tensile strengths of six specimens, including three repaired specimens and three pure cracked steel specimens, were evaluated. The test outcomes indicated that the bolt repairing method significantly enhanced the tensile strengths of the cracked steel plates. As an example, the failure of a pure steel plate with a 1 mm width crack occurred at 813 N, whereas after being repaired, a tensile strength of 1298 N was observed. Based on finite element (FE) analysis, the influence of bolt preloads and interfacial friction coefficients were verified. The stress-relative ratio for specimens was contingent on the bolt preload magnitude and gradually decreased as the preload was augmented. By exploring the repairing effect for varied friction coefficients, it was concluded that using a higher bolt preload can aid in eliminating the performance discrepancy of the overall component caused by interface treatment errors.

A Simplified Analytical Model for FRP-Strengthened Curved Brittle Substrates Using the Multi-Linear Bond-Slip Law

The utilization of fiber-reinforced polymer (FRP) composites for building reinforcement has gained widespread acceptance. However, the bond behavior between externally applied composites and strengthened substrates, which are crucial for system efficacy, has primarily focused on flat surfaces. Yet, the challenge of curved substrates, common in masonry arches and vaults, remains less explored. This study introduces a classical analytical model addressing the bond behavior between FRP plates and curved substrates. This classical approach is structured upon a simplified model that concentrates all the non-linearities of the FRP–substrate interface. The interface is described through a universal multi-linear stress–slip relationship, with the influence of the curved substrate being considered by the normal stress that impacts the interface law. Closed-form solutions for distinct bond-slip law stages are derived and verified against the previous study. Through comparisons with existing experimental data and simulations, this approach is able to predict the maximum load, the trends of the global load-slip curves, and give insights into detailed local behavior. Additionally, the exploration of employing neural networks for determining the interface law exhibits promising outcomes.

A review on flexural behavior of reinforced concrete beams strengthened with prestressed carbon fiber reinforced polymer plates

In recent years, with the rapid development of China’s economy, reinforced concrete structure as an economical and good mechanical properties material, is widely used in buildings. In bridge engineering, Carbon Fiber Reinforced Polymer materials is mostly used as externally bonded reinforcement for flexural strengthening of reinforced concrete (RC) beams. However, this method makes the strength of CFRP plates cannot be fully utilized, while the prestressed technology can significantly improve the efficiency of CFRP materials and the flexural strength of the RC beams. This paper compares different methods of prestressed CFRP plates strengthening RC beams and discuss the development of the technology. The results shows that RC beams strengthened with prestressed CFRP plates have better flexural performance. The cracking, yield and ultimate loads increase significantly compared with ordinary beams or non-prestressed strengthened beams. The effectiveness of strengthening process are related to many factors ranging from anchorage methods, prestress levels, ratio of corrosion to bond length. Future research suggestions are also given. At present, most of the experiments are operated in ordinary environment, which is different from the project in real life. More testing environment like chlorine corrosion must be considered. The trials about prestress loss during strengthening process are not enough. There also need more comparative trials in prestressed CFRP plates strengthening concerning prestress loss and non-prestressed CFRP plates.

Energy absorption of polyurethane filled Al 6061 honey comb sandwiched structure

The energy absorption characteristics of composites are developed for applications likely to be subjected to sudden or prolonged impacts. In lightweight applications, the possibilities of Al 6061 composites are being explored with various known materials with similar properties. Three materials of low densities but high strength was combined: hexagonal honeycomb Al 6061 core was sandwiched with polyurethane foam and embedded within two glass fiber-reinforced polymer plates. L-9 orthogonal array Taguchi DOE was adopted for the design of the experiment varying the polyurethane mixture, core height, and face sheet thickness using the three-factor method. From the output of the Taguchi DOE, twenty-seven samples were fabricated. In order to determine the force-displacement relationship for each of the test samples, a three-point bending test was performed on a universal testing machine. Energy absorption (EA) and crushing force (CF) were determined from the force and displacement values. These values were then optimized to minimize the PCF while maximizing EA. Numerical analysis performed correlated with the results from experimental samples after testing. Since energy absorption is a measure of applied force and the resulting displacement on a material, the energy absorption characteristics were discussed.

Numerical and experimental investigation on the flexural stiffness of RC beams strengthened with prestressed CFRP plate exposed to wetting/drying cycles

The load-deflection relationship is critical for the serviceability and structural durability of reinforced concrete (RC) structures strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates. This study aims to investigate the impact of prestressing levels and wetting/drying cycles (WDCs) on the flexural stiffness of prestressed CFRP-strengthened RC beams. A modified flexural stiffness prediction model was proposed by incorporating prestressing levels, interfacial bond slip, and softening after WDCs. Subsequently, four-point bending tests were conducted on 11 strengthened beams with different prestressing levels and WDCs to estimate flexural behavior. The results suggest that WDCs can adversely affect the flexural stiffness of the strengthened beams, particularly for the post-cracking stiffness of the non-prestressed specimens. However, prestressed strengthening can mitigate the stiffness degradation caused by WDCs. Moreover, a finite element (FE) model utilizing a traction separation model can accurately predict flexural stiffness. Finally, the flexural stiffness was computed using both the existing and proposed models and the proposed model provides the closest prediction of the flexural stiffness for CFRP-strengthened beams under WDC and prestressing.

A robust and efficient 3D mixed-mode cohesive interface model for predicting the debonding failure in FRP strengthened concrete structures

A new and practical cohesive zone model (CZM) considering the coupling between damage mechanics and plasticity is proposed to facilitate structural-scale finite-element (FE) simulations for concrete members strengthened with fiber-reinforced polymer (FRP). The model dwells on an adaptive sub-stepping technique to overcome common convergence difficulties during mixed-mode debonding between FRP and concrete. Additionally, it automatically adjusts the computational time increment based on the convergence performance of Newton-Raphson iterations, ensuring efficiency by applying time stepping selectively to critical integration points with diverging problems. Moreover, the model introduces a transformation between effective stress and nominal stress to enhance numerical stability when dealing with complex interfacial behaviors like stiffness degradation, plastic deformation, dilation effects, and mixed-mode failure. Thus, the paper’s novelty lies in the development of a stable and versatile 3D interface model achieved through advanced numerical optimization techniques. The resulting FE models have accurately reproduced various failure modes, such as FRP-concrete debonding and local buckling of FRP plates, demonstrating a high level of reliability and computational efficiency.

Spatial and Temporal Deep Learning in Air-Coupled Ultrasonic Testing for Enabling NDE 4.0

Air-coupled ultrasonic (ACU) testing has been used for several years to detect defects in plate-like structures. Especially, for automated testing procedures, ACU testing is advantageous in comparison to conventional testing. However, the evaluation of the measurement data is usually done in a manual manner, which is an obstruction to the application of ACU testing. The goal of this study is to automate and improve defect characterization and NDE 4.0 accordingly with deep learning. In conventional ACU testing the measurement data contains temporal (A-scans) and spatial (C-scans) information. Both data types are investigated in this study. For the A-scans, which represent time series data, neural network architectures tailored to such data types are applied. In addition, it is evaluated if further adaptions of the training procedure increase the performance. The C-scans are segmented by applying different U-net similar architectures and training strategies. In order to use spatial and temporal information, a further approach is taken. The prediction of the time series models is segmented with image models. The performance of all trained models and training strategies is compared with the F1-score and benchmarked against the conventional evaluation, which is thresholding of the C-scans. As specimens, artificial defects in acrylic and carbon fiber-reinforced polymer plates are investigated.

Analytical solution of the full-range behavior of adhesively bonded FRP-steel joints made with toughened adhesives

Fiber-reinforced polymer (FRP) composites represent an effective solution to strengthen and retrofit existing steel members. Namely, bonded or unbonded carbon FRP (CFRP) plates have been employed to improve the strength, fatigue behavior, and durability of steel bridges. In bonded solutions, the effectiveness of the CFRP reinforcement strongly depends on the adhesive employed to bond the plate, as failure usually occurs due to debonding. Within this framework, the use of toughened adhesives is particularly attractive since they may improve the load carrying capacity of the CFRP-steel interface, also providing a certain ductility. Debonding in CFRP-steel joints was previously studied using a cohesive approach. However, solutions able to describe the full-range behavior of joints with toughened adhesives and finite bonded length are not available in the literature. In this paper, a trapezoidal (trilinear) cohesive material law (CML) is employed to model the bond behavior of pultruded carbon FRP-steel joints made with a rubber-toughened epoxy adhesive, which showed cohesive debonding within the adhesive layer. The analytical solution provided is employed to study the experimental response of nine CFRP-steel joints tested using a single-lap direct shear set-up. Comparisons of analytical and experimental results of joints with three different bonded lengths confirm the effectiveness of the solution proposed.

Shear transferring mechanism of the FPR-to-concrete bonded joint with end U-jacketing: A theoretical study

Installation of fiber reinforced polymer (FRP) U-jackets is an effective method for improving the low utilization rate of the expensive FRP material in the application of flexural strengthening of the reinforced concrete (RC) beam. The stress transfer mechanism of the FPR-to-concrete bonded joint with end U-jacket still remains poorly understood. This study proposed a new analytical model to predict the interfacial debonding process and the load carrying capacity of the joint with end U-jacket. The failure process of the FRP-to-concrete joint with an inclined U-jacket features five stages including elastic, elastic-softening, elastic-softening-debonding, softening-debonding and completely debonding stages. Expressions for the interfacial shear stress distribution and load–displacement relation are derived for these five stages. The load–displacement curve predicted by the analytical model, indicating that the bearing capacity of the joint with end U-jacket has increased by 200%, is in good agreement with the experimental and FE analysis results. Finally, the results from analytical solutions are presented to clarify the effects of the bond length, the FRP plate stiffness and the elasticity coefficient of end U-jacket on the load–displacement relations, the ultimate load and the effective bond length.

Study on Effects of Geometric Parameters on Tensile Strength of Hybrid Bonded-Rived Joint of Fiber Reinforced Polymer Plates

Hybrid bonded-rived joint combines bonding and riveting and has become one of the most important connection forms in composite materials. This paper investigates and analyzes the influence of geometric parameters of CFRP hybrid bonded-rived joints on load-bearing strength. The finite element method is used to analyze the strength of the hybrid bonded/riveted joint between carbon fiber composite and metal under tensile load. The different ratios of the hybrid joint’s e/D, w/D, and w/e are analyzed. It is shown that e/D and w/D significantly impact damage loads and failure mode of the hybrid bonded/riveted joint. The increase of e/D will change the joint from shear-out to net tension failure, and the effect of w/D is opposite to that of e/D. Under the same bonding area, different w/e impacts the damage load of the joint, and the larger w/e makes the joint have a larger failure load, and the stiffness of the joint is also large.

Bond behavior of FRP-concrete wet-bonding interface under lateral confinement

Wet-bonding is a technique of connecting fiber reinforced polymer (FRP) profile and cast-in-place concrete, which is characterized by the simultaneous hardening of concrete and adhesive. The mechanical properties of wet-bonding interface have been investigated by researchers, but none of them considers the influence of lateral confinement which is commonly present in structures. The insufficient knowledge on wet-bonding consequently hinders its application in FRP-concrete hybrid structures. To this end, this paper investigates the bond properties of wet-bonding interface in confined concrete through pullout and pushout tests. Test results indicate that the interfacial behavior of wet-bonding interface can be divided into three stages. In the first stage, the interfacial resistance comes from the chemical bond of adhesive, and the lateral confinement is hardly activated. This stage comes to an end when the interface between adhesive and concrete fails. In the second and third stage, the interfacial resistance is mainly contributed by the friction between fractured surfaces of adhesive and concrete. The relative movement of fractured surfaces which are microscopically rough induces vertical movement and then activates the lateral confinement, resulting in lateral pressure and tangential friction. The significant friction behavior further damages the FRP-adhesive interface, leading to the final delamination of adhesive from the FRP plate. Based on the above force-transfer mechanism, a bond stress-slip model depending on the lateral pressure is developed. This interfacial model is implemented into Abaqus and its effectiveness is verified by comparing with test results.

Compression performance of composite plates after multi-site impacts: A combined experimental and finite element study

This paper reports on a study of the damage tolerance of carbon fibre reinforced polymer plates, used in aircraft fuselage, subjected to multi-site impacts. A new fixture was designed to perform sequential low-velocity impacts at different locations on plates with two different thicknesses, representing upper and lower fuselage panels. The residual strength in compression was measured using a new compression-after-impact rig designed to prevent global buckling of thin plates. Experimental results indicated that compared to single impacts, multi-site impacts can reduce the residual strength of the thin plates, but not the thick plates. To explain this difference, a detailed finite element model was developed, which enabled modelling of multi-site impacts and compression after impact in one simulation. Simulations suggested that the second impact damage changes the buckled shape prior to failure for the thin plates. A parametric analysis on key material parameters showed that they have a small effect on the residual compressive strength. This work can help to improve the design of aircraft panels with respect to threats posed by multi-site impacts.